.. these chips are used across different manufactures like Texas Instruments CC2500 RF Chip used by JR DMSS, HiTec, Corona, FrSky, Tactic, Futaba S-FHSS, Skyartec, futaba and FrSky use the same chip

Sorry thats not true. JR DMSS is ZigBee 802.15.4 its not the cc2500

the most widely deployed enhancement to the 802.15.4 standard is ZigBee standard , which is a standard of the ZigBee Alliance. The organization maintains, supports, and develops more sophisticated protocols for advanced applications. So Zigbee 802.15.4 is not a RF chip it is something it uses... so what chip does it use then?

CC2520. (a completely different animal animal, even though numerically it sounds similar.

I heard of a case where it is possible to adjust the TX output power on open source radios by reprogramming the RF chip. If the power is increased by tinkering with the code and this consequently causes interference to other users who then is liable. More to the point how would you ever prove it.

A.

Since the programming for the RF chip is not open source but manufacturer's software, then I cannot see any worse problem than with any other make of transmitter.

Andy48

I will try to find the original document that explains how this was done. Not necessarily through the normal open source route but still possible with a little research.

The document I referred to above appears as a email circulated by Duncan McClure South Midalnds Area Delegate to the BMFA and recommends that a local club adopts an embargo of open source radios as he maintains it IS possible to change the power settings using this system.

I have now seen this email but it is an internal club communication so I won't put it online without permission.

Whilst it may (in theory) be possible to increase the power output of any system (even 35 MHz!), the extra output available at 2.4 GHz is trivial.

Going from 100 to 200 mW may sound a lot, but a more accurate way of perceiving it is by the dBm figure. 100mW=20dBm, 200mW=23dBm. The dBm figure is a far more realistic way of imagining the increase.

You will get a similar increase just by replacing the standard antenna (2dB gain) with a "high gain" one (typically 5dB gain - a similar 3dB increase!), without ever having to adjust the Tx at all. And that applies to ANY transmitter, Open Source or not.

All the transmitters I have looked at have a typical output of 60mW. The 2dB gain of the antenna raises this to 100mW erp (Effective Radiated Power). It does this by concentrating the RF output in a specific direction, a bit like a torch bulb being "brightened" by placing a reflector behind it - but only in a specific direction.

The higher the gain of the antenna, the more directional it becomes, so higher gains do not necessarily improve performance in our application.

Note: What I am talking about here is "squishing" the doughnut shaped radiation pattern of a typical RC antenna, ie: making the "dead spot" off the tip deeper and wider.

In practice, yes, increasing the output of the transmitter by either a firmware tweak (not trivial!) or using a higher gain antenna (simple!) does break the regulations.

The likely impact of a 3dB increase in power on other users in a typical model club environment approximates to - er - zero! The likely advantage of such an increase to the user approximates to - er - zero! In the case of high gain antennas, the narrower beam of the signal may well prove detrimental!

Note that I am NOT recommending modifying the RF output of our transmitters. 100mW / 20dBm is more than adequate for our purposes, and increasing it does not do our reputation with the powers-that-be any good, at a time when we need all the friends that we can get!

The only system I know of that actually offers 200 mW is (or was?) Spektrum - which is NOT open source! The US versions do - or certainly did at one time - use 200mW, as permitted by FCC regulations. EU versions are restricted to 100mW, but of course if someone grey imports a US spec set........

If anyone wanted to increase the power output, they could do it to ANY transmitter by adding a signal amplifier and patch antenna. I'm betting that there are commercially available WiFi signal amplifiers that would do the job.

Is the club that is banning open source radios going to ban ALL transmitters because it's possible to increase the power output of these too?

The document I referred to above appears as a email circulated by Duncan McClure South Midalnds Area Delegate to the BMFA and recommends that a local club adopts an embargo of open source radios as he maintains it IS possible to change the power settings using this system.

I have now seen this email but it is an internal club communication so I won't put it online without permission.

You may want to contact Duncan directly on this subject.

Andy.

I have over 20 transmitters, all running open source firmware. Apart from the 4-in-1 module, they all use a 2.4 GHz RF module that is closed source firmware provided by the original manufacturer and the open source firmware has NO access to the RF chip programming.

The document I referred to above appears as a email circulated by Duncan McClure South Midalnds Area Delegate to the BMFA and recommends that a local club adopts an embargo of open source radios as he maintains it IS possible to change the power settings using this system.

I have now seen this email but it is an internal club communication so I won't put it online without permission.

You may want to contact Duncan directly on this subject.

Andy.

I have over 20 transmitters, all running open source firmware. Apart from the 4-in-1 module, they all use a 2.4 GHz RF module that is closed source firmware provided by the original manufacturer and the open source firmware has NO access to the RF chip programming.

Mike

Mike.

I think that THIS is the sort of tweaking that Andy S is referring to. Info is out there if anyone really wants to do it, but as the thread in the link alludes to, it doesn't make sense to do it.

Still not open source is it, that's hacking the RF firmware or adding alternate non-CE approved aerials or hardware amplifiers! That could equally apply to any brand you care to mention, open source or otherwise.

Well, the FrSky XJT module uses 3.3V to power the SE2431L power amplifier chip, so you could only try to increase the output power by increasing the supply voltage to (the absolute maximum voltage for the device of) 3.6V.

Then you could see an output power increase from 22.5 to 24 dBm, but only if you also increase the input signal by 3dBm (from 0dBm to 3dBm). Since the input signal is that provided by the CC2500 chip, and that can only output a maximum of +1dBm, you can't do that! In any case, the output power from the CC2500 is controlled by the (non-open source) firmware in the module.

I can't actually see that suggestion achieving anything significant, while risking exceeding the max. supply voltage of 3.6V and destroying the SE2431L

At best, I reckon you might get a 0.5dBm gain in output power, so increasing the output from 100mW to 112mW, which might get you an extra 6% of range!

People have been hacking into Tx OS software since just after computer controlled Tx's came out.

I knew a chap who over 20 years hacked into a JR PCM 10 Aero and sucked the aero code off of it and then wrote that into a JR PCM 10 heli and was able at the flick of a switch go between aero and heli software.

I do remember the chap saying that about 75% of the code was to run the GUI screen.